The field is internal combustion engines. Particularly, the field includes two-stroke, opposed-piston engines with ported cylinders in which fuel injectors are supported for direct fuel injection through the sidewalls of the cylinders. The support structure positions a fuel injector at a compound angle with respect to a cylinder in that its longitudinal axis is tilted at one angle with respect to a first plane that contains the longitudinal axes of all cylinder bores and is also tilted at another angle with respect to a plane that is orthogonal to the first plane and passes through diametrically opposed injector ports in each of the cylinders.
As seen in FIG. 1, an internal combustion engine is illustrated by way of an opposed-piston engine that includes at least one cylinder 10 with a bore 12 and longitudinally displaced exhaust and intake ports 14 and 16 machined or formed therein. The exhaust and intake ports 14 and 16 each include at least one circumferential array of openings in which adjacent openings are separated by a solid bridge. In some descriptions, each opening is referred to as a “port”; however, the construction of a circumferential array of such “ports” is no different than the port constructions shown and described herein. Fuel injector nozzles 17 are located in or adjacent to injector ports that open through the side of the cylinder, at or near the longitudinal center of the cylinder. Two pistons 20, 22 are disposed in the bore 12 with their end surfaces 20e, 22e in opposition to each other. For convenience, the piston 20 is referred as the “exhaust” piston because of its proximity to the exhaust port 14; and, the end of the cylinder wherein the exhaust port is formed is referred to as the “exhaust end”. Similarly, the piston 22 is referred as the “intake” piston because of its proximity to the intake port 16, and the corresponding end of the cylinder is the “intake end”.
Operation of an opposed-piston engine with one or more cylinders such as the cylinder 10 is well understood. In this regard, and with reference to FIG. 2, in response to combustion occurring between the end surfaces 20e, 22e the opposed pistons move away from respective top dead center (TDC) positions where they are at their closest positions relative to one another in the cylinder. While moving from TDC, the pistons keep their associated ports closed until they approach respective bottom dead center (BDC) positions in which they are farthest apart from each other. The pistons may move in phase so that the exhaust and intake ports 14, 16 open and close in unison. Alternatively, one piston may lead the other in phase, in which case the intake and exhaust ports have different opening and closing times.
In many opposed-piston constructions, a phase offset is introduced into the piston movements. For example, presume the exhaust piston leads the intake piston and the phase offset causes the pistons to move around their BDC positions in a sequence in which the exhaust port 14 opens as the exhaust piston 20 moves through BDC while the intake port 16 is still closed so that combustion gasses start to flow out of the exhaust port 14. As the pistons continue moving away from each other, the intake port 16 opens while the exhaust port 14 is still open and a charge of pressurized air (“charge air”) is forced into the cylinder 10, driving exhaust gasses out of the exhaust port 14. The displacement of exhaust gas from the cylinder through the exhaust port 14 while charge air is admitted through the intake port 16 is referred to as “scavenging”. Because the charge air entering the cylinder flows in the same direction as the outflow of exhaust gas (toward the exhaust port), the scavenging process is referred to as “uniflow scavenging”.
As per FIG. 1, the pistons move through their BDC locations and reverse direction, the exhaust port 14 is closed by the exhaust piston 20 and scavenging ceases. The intake port 16 remains open while the intake piston 22 continues to move away from BDC. As the pistons continue moving toward TDC (FIG. 2), the intake port 16 is closed and the charge air in the cylinder is compressed between the end surfaces 20e and 22e. Typically, the charge air is swirled as it passes through the intake port 16 to promote good scavenging while the ports are open and, after the ports close, to mix the air with the injected fuel. Typically, the fuel is diesel which is injected into the cylinder by high pressure injectors. With reference to FIG. 1 as an example, the swirling air (or simply, “swirl”) 30 has a generally helical motion that forms a vortex in the bore 12 which circulates around the longitudinal axis of the cylinder. As best seen in FIG. 2, as the pistons advance toward their respective TDC locations in the bore 12, fuel 40 is injected through the nozzles 17 directly into the swirling charge air 30 in the bore 12, between the end surfaces 20e, 22e of the pistons. The swirling mixture of charge air and fuel is compressed in a combustion chamber 32 defined between the end surfaces 20e and 22e when the pistons 20 and 22 are near their respective TDC locations. When the mixture reaches an ignition temperature, the fuel ignites in the combustion chamber, driving the pistons apart toward their respective BDC locations.
As illustrated in FIG. 2, fuel is directly injected through the side of the cylinder (“direct side injection”) into the combustion chamber 32 and the movement of the fuel interacts with the residual swirling motion of the charge air in the combustion chamber. In some aspects of opposed piston engine construction with direct side injection, it is impractical to position the fuel injectors so that their axes are in diametrically opposing alignment. In this regard, physical constraints arising from an engine construction with multiple cylinders disposed in a row limit the space available for fuel injector placement.